(i) Field of the Invention
The present invention relates to a filter apparatus for condensing and separating plankton from sea water, so as to use the plankton as a natural feed for an ocean culture or to return the plankton back to sea water to protect marine livings and at the same time to use the filtrate as cooling water in power plants or as fresh water purified from sea water.
(ii) Description of the Prior Art
A large amount of cooling water is used in steam and atomic power plants to cause a steam condenser to condense, into water, steam used for turbine rotation. A typical example of a cooling water source is sea water, which is an inexhaustible source. However, since various types of marine living organisms and substances having various shapes and sizes are contained in sea water, the water must therefore be filtered by a settling basin or a strainer. The filtrate as a cooling medium is then supplied through a water supply pipe to the steam condenser. FIG. 3(a) is a block flow chart illustrating the pretreatment of salt water. Sand particles and shells mixed in with salt water entering through inlet port 1 are removed by settling basin 2. Large objects are then removed by bar screen 3, and relatively small objects are removed by rotary screen 4. The filtrate is then supplied to steam condenser 6 through water supply pipe 8. However, in the course of the conventional pretreatment, marine microorganisms such as plankton living in salt water cannot be captured or removed. Thus, the plankton are conveyed to condenser 6 through pipe 8, and larvae of Mussels (Mytilus edulis) and Balanus become adhered or attached to the inner wall surfaces of pipe 8 and condenser 6. In the worst case, the larvae form a 20 cm thick layer on the inner wall surface, clogging the water channel and thus decreasing the amount of water supplied and degrading the heat exchange efficiency. In addition, the heat exchange pipe becomes clogged up with peeled-off shells, and the power generating efficiency is degraded. In order to perform periodic maintenance, a chemical containing free chlorine is used to weaken shells attached to the inner wall surfaces, and the weakened shells being removed by peeling them off. Another conventional maintenance procedure is to apply an anticontamination paint containing copper suboxide and an organic tin compound having a high toxicity to the inner wall surfaces of pipe 8 and condenser 6, thereby preventing adhesion of shells thereto.
Since the above-mentioned maintenance procedures must be performed on a large-scale basis, each time a water supply pump has been deactivated, this results in high maintenance costs. In addition, the marine living organisms may be totally annihilated by the process. In an application of the anticontamination paint, the concentration and thickness of the paint that can be applicable are limited, and its effectiveness period is short. In addition, the mechanical strength and adhesion strength of the paint film are not satisfactory. As a result, the desired effect is not always obtained. In addition, marine living organisms such as fish, shells, and sea weed become contaminated by such a paint, which gives rise to environmental pollution. In recent years, this environmental pollution poses a problem that should be immediately solved.
Larvae of organisms such as Mussels attach themselves to the surfaces of various equipment by means of a sticky disk formed by the hardening of secretory materials from their byssuses. Therefore, use of a microstrainer made of a material having a low interface tension, such as silicon and Teflon, has been proposed for the purpose of preventing attachment of larvae to equipment surfaces. In this case, however, a slime or the like becomes attached to the inner wall surfaces, and good surface conditions cannot be maintained. The slime or the like adheres to the strainer, causing it to become clogged. We are confronted with a circumstance wherein the ocean culture of fishes and shells must be widely prevailed to assure the ocean protein sources due to limitations of fishing grounds. However, the conventional techniques are incapable of assuring the supply of a low-cost natural live feed required for the ocean culture.